The girlfriend of Stephen Paddock has given a statement on his actions, saying she had no idea he was planning this.
Paddock, 64, killed 59 and injured more than 500 after he opened fire on revelers at an open air festival in Las Vegas from his room in the neigbbouring Mandalay Bay hotel.
Paddock was found dead in the room, and over the course of the investigation, police had named Marilou Danley - his girlfriend - as a person of interest.
She voluntarily returned from the Philippines, where she had been at the time of the incident in Nevada, and was met by FBI agents at Los Angeles International Airport.
Danley has released a statement to say she had no idea Paddock - who she described as "quiet and kind" - had been preparing to commit an atrocity.
She expressed shock at the "unspeakable violence" he had committed, saying she had loved him and wanted a "quiet future" together.
The incident in Las Vegas is the bloodiest shooting in US history, and the motives for it remain unclear.
Investigators have found no clear links to terrorism, despite a claim of responsibility by Islamic State.